The thermal isomerization of bicyclo [3,2,0]-hept-6-ene has been studied in the gas phase and in solution in the temperature ranges 274-327" and 256-288" respectively. In both phases the reaction was kinetically first order and yielded only one product, cyclohepta-173-diene. From the rate constants obtained at a number of temperatures in each temperature range the following Arrhenius equations were calculated : kgas = 1014.31 exp ( -45,51O/RT) sec-1, ksolution = 1014.65 exp (-45,86O/RT) sec-1.The experimental results indicate that this isomerization, like the other cyclobutenes so far investigated in detail, is a true unimolecular reaction.

802EIlCHI HANAMURA may be modified by stretching vibrations. If this modification is stronger than the deviation of the stretching vibrations from the adiabatic approximation, it will have stronger Raman scattering than other stretching vibrations which do not participate in modification of charge transfer. This effect has been observed by Ito et at. in the ICI crystal. 20On the basis of these theoretical results, it is thus concluded that Raman scattering is a useful device for studying the details of the charge-transfer mechanism.The photoelectron spectra of ethylene and ethylene-d4 have been measured using a new high-resolution spectrometer and the 584-A helium resonance line as a light source. Five ionization potentials have been observed for each compound. Vibrational structure associated with the transitions leading to the first and fourth ionization potentials has been resolved, and it has been possible to assign the corresponding vibrational modes. The photoelectron spectrum of neon, obtained with the 537-A line from the same light source, is also presented.

No abstract

The thermal isomerizations of cis and trans-l,2,3,4-tetramethylcyclobutene and bicyclo[4.2.0]oct-7-ene have been studied in the gas phase. In the temperature range 157-2Ol0C, cis-tetramethylcyclobutene isomerizes by a homogeneous first-order process to yield cisYtrans-3,4-dimethylhexa-2,4diene and the rate constants fit the Arrhenius equation kl = 1014.10 exp (-37,360IRT) sec-1.In the temperature range 125-167°C the trans tetrametliylcyclobutene isomerizes to trans,trans-3,4dimethylhexa-2,4-diene, but under the conditions employed this product undergoes surface-catalyzed polymerization. The rate of disappearance of the reactant obeyed first-order kinetics and the rate constants obtained fitted the Arrhenius equation, k2 = 10*3.85 exp (-33,59O/RT) sec-1. The isomerization of bicyclo[4.2.0]oct-7-ene yields cycloocta-l,3-diene by a homogeneous first-order process, and in the temperature range 236-285" the rate constants fit the Arrhenius equation, k3 = 1014.13 exp (-43,18O/RT) sec-1.Above 1 mm the rate constants of the three isomerizations are independent of pressure. The results obtained are compared with those for other cyclobutenes with special reference to the mechanism of the transformation.

The ionisation potentials of the phosphonitrilic fluorides (NPF2), (n = 3-8) have been measured by photoelectron spectroscopy, and those of other phosphonitrilic derivatives (NPX2)n [X = CI, n = 3-7; X = OCH,*CF,, OMe. OPh, NMe,, or Me, n = 3 or 41 by electron impact. All the 6-membered cyclic compounds have first ionisation potentials which are higher than those of their 8-membered analogues, and in the fluorides the first ionisation potentials alternate as the size of the ring increases beyond 8 atoms. These results, and also the relative energies of a number of states of ( NPF2),+, are interpreted by use of the orbital approximation and a model of a dual r-system which involves 3d-orbitals at phosphorus and valence-shell orbitals of nitrogen and which supplements the underlying o-framework. Comparison of the results with simple molecular orbital calculations suggest that the highest r-system is of the homomorphic type, involving mainly the 3dz~-y:-orbital, and that it is accompanied by a lower and partly overlapping heteromorphic system, to which the 3dzz-orbital makes the major contributions. Ionisation spotential are also assigned to molecular orbitals which span the P-N and P-F a-bonds, and the fluorine lone pairs.